Weber Tore-Vibe

[Diablo]

My kit arrived and everything is there except the cathode resistor for V3 (6V6GT). Weber sent a 1K- half watt instead of a 1K- 5 watt. I don't have any 5 watt resistors in my inventory, but I do have a 3 watt (vitreous enamel power resistor). Is the the 3 watt OK to use or am I living dangerously?

Here's the link to the layout:
https://taweber.powweb.com/store/5h15t_layout.jpg

[tubeswell]

The way the reverb driver is set up, with a 6V6 you get about 24mA-27mA tube current with a 1k resistor in that circuit, which is about 0.5W-0.7W. So a 2W resistor should be sufficient. (I wouldn't use 0.5W - or even 1W - tho')

[Diablo]

Thanks tubeswell for the quick answer. I wasn't quite sure how much current the tube would draw. Now I'll get to soldering.

[tubeswell]

Well (as you know) the tube current depends on the plate and screen voltage, but is indicated by the cathode voltage divided by the cathode resistance. The current I gave you was approximate. If you look at the 6G15 schematic, which has a B+ of 295V, it has 24V idling at the cathode (which if you have a perfect 1k resistor, is 24mA tube idle current, and the resistor would dissipate about 0.6W at idle). Bearing in mind that the 6G15 had a 6K6GT, and the Revibe has a 6V6GT, it could be anything in that range - maybe a bit more.

Ideally you want to drive the pan with as much current as you can without burning out the transducers, so you possibly could drive it a bit harder than that, but its a bit of suck it and see. If you were using an 8K Primary-Z on the reverb tranny maybe I would be cautious about running the driver tube too hard (because that translates into even more current going into the pan). FWIW I used a type 4 accutronics pan and a 5k5-8R tranny with a 6V6 driver idling at 25.5mA (338V on the plate) in my recent 6G15 build, and it sounds good enough for me.

[Diablo]

OK, a few more questions on power tube current. My 6K6GT tube measures 25.9 volts on pin 8, and 351 volts on pin 3. I calculate 9 watts at idle. Since the 6K6 is rated for 8.5 watts max dissipation, should I increase the value of the cathode resistor to avoid tube saturation? Or just stick in a 6V6, rated for 12 watts dissipation? Could I stick in a 6L6, or would that draw too much current through the transformer?

[tubeswell]

OK, a few more questions on power tube current. My 6K6GT tube measures 25.9 volts on pin 8, and 351 volts on pin 3. I calculate 9 watts at idle. Since the 6K6 is rated for 8.5 watts max dissipation, should I increase the value of the cathode resistor to avoid tube saturation? Or just stick in a 6V6, rated for 12 watts dissipation? Could I stick in a 6L6, or would that draw too much current through the transformer?

So your resistor isn't quite 1K? Doesn't matter - more current is all the better to drive the pan with. I wouldn't be concerned about .5W extra on the 6K6 myself. But if it bothers you then try a 6V6 and see if you like the sound better. (Or you could zener the B+ down to around 300V)

I wouldn't bother with a 6L6.

[mazzbob]

Hello, Happy Holidays to all:

I have compiled almost all the parts to build a Tore-T reverb unit. The only parts I still have to obtain are for the diode rectifier/ the thermistor/ tank and tubes. Does anyone have the values for these parts for the diode rectifier and thermistor specifically, I can't find the values ? I guess I could get them through Weber along with the tank and tubes I just trying to cut costs on the shipping fees.

[tubeswell]

You won't cut much cost on shipping by excluding some diodes and thermistors. The diodes will be 1N4007 or (1000V 1A) equivalent. What are the thermistors for? Mains surge protection?

[mazzbob]

tore-vibe

The only thing I can think of, that's what makes it a vibrato. [IMG]www.taweber.powweb.com/store/kits_weber.htm#5H15T[/IMG]
If I am correct ( I may not be) the themistor reacts to heat which alters voltage I guess the hotter it gets the faster it alters the output votage that causes the vibrato to work.

It's in the layout at http://www.taweber.powweb.com/store/...eber.htm#5H15T

Thanks for the diode values now I have to find the thermistor value or just go through weber for the tank, tubes, thermistor and diode bridge. I have most all the other parts just lying around from other projects and amps that I've worked on.

Has anyone built one of these units successfully?

[Diablo]

No, the thermistor is just to give a slow turn on to let the tube filaments heat up before the B+ hits 'em. The thermistor goes between the bridge rectifier and the choke. The Tore-vibe has a bias varying tremolo. It uses a tube oscillator V5. Some signal is fed back to the tube to cause it to oscillate. When the tube oscillates it changes the cathode bias of V4 because the cathodes of V4 and V5 are connected. By changing the bias of V4 in an oscillating manner, this raises and lowers the volume - creating tremolo.

[Bruce / Mission Amps]

No, the thermistor is just to give a slow turn on to let the tube filaments heat up before the B+ hits 'em. The thermistor goes between the bridge rectifier and the choke. ...

Well, kind of... the thermistor is really to limit inrush current.... it's turn on time is way to fast to allow any tubes to warm up.
I used the Thermistor in the 5F2H amps because it originally used a small, 400v@1a, encapsulated, full wave bridge SS rectifier device, which would shoot a full boat load of current into the first filter cap and we I thought it might be a good idea to reduce that high current shock a tiny bit since the project also used fairly inexpensive parts and 450v Asian power supply caps of untested quality.
I can only assume this is also why you see the Thermistor used in the other projects with a FWB SS rectifier.... etc.
I being willing to bet it doesn't really need it and you might be better served with a 22 to 47 ohm 2 watt resistor in series, or both.

[TD_Madden]

Yes, there's one in my '66 Vox AC50.....seems like it wouldn't be enough to slow the inrush voltage a bit.